Description

Fixes #7517.

When a chord follows another task in a chain, the tracer passes priority=None if parent-priority inheritance is disabled. The chord clones its body with that value, erasing the body's configured priority. For example, a body with priority=2 reaches the backend with priority=None.

Dismiss None call options before cloning the chord body, matching Signature.apply_async(). Explicit priorities, including zero and inherited parent priorities, continue to override the stored value. Adds 12 parametrized cases covering direct chord dispatch and the actual task-tracer-to-chord path, plus a changelog entry.

Validation on upstream base 79baa09f2fe08c0aa455b60191b96f6809655282:

• New cases before the fix: 4 failed, 8 passed. All 12 pass with the fix.
• pytest t/unit/tasks -q: 1,202 passed, 1 skipped, 1 xfailed, plus 27,629 passing subtests, on both Windows/Python 3.12.13 and Linux/Python 3.12.3.
• Repository pre-commit checks pass for the changed files, including pyupgrade, flake8, isort, spelling and mypy.
• Unfiltered Bandit 1.9.4 scans of the base and changed production trees report the same 49 findings, with identical file, code, line, severity and confidence; no new findings. The repository's historical bandit.json cannot be loaded by this Bandit version (issue_cwe is missing). No security configuration or checks were changed.

Tests use the in-memory transport/backend. External broker integration tests and the full Python-version matrix were not run locally.

AI assistance: OpenAI Codex prepared the patch, regression tests and this draft on Dcastroro's behalf. Human review is pending.